In electrophotography an image comprising an electrostatic field pattern, or latent image, which is usually of non-uniform strength, is formed on an insulative surface of an electrophotographic element. Such an element includes a photoconductive layer and an electrically conductive substrate. The electrostatic latent image is usually formed by imagewise radiation-induced dissipation of the strength of portions of an electrostatic field of uniform strength previously formed on the insulative surface. Typically, the electrostatic latent image is then developed into a toned image by contacting the latent image with an electrographic developer. If desired, the latent image can be transferred to another surface before development.
In latent image formation, the imagewise radiation-induced dissipation of the initially uniform electrostatic field is brought about by the creation of electron/hole pairs, which are generated by a material, often referred to as a photoconductive or charge-generation material, in the electrophotographic element in response to exposure to imagewise actinic radiation. Depending upon the polarity of the initially uniform electrostatic field and the types of materials included in the electrophotographic element, part of the charge that has been generated, i.e., either the holes or the electrons, migrate toward the charged insulative surface of the element in the exposed areas and thereby cause the imagewise dissipation of the initial field. What remains is a non-uniform field constituting the electrostatic latent image.
Several types of electrophotographic recording elements are known for use in electrophotography. In many conventional elements, the active photoconductive materials are contained in a single layer. This layer is coated on a suitable electrically conductive support or on a non-conductive support that is overcoated with an electrically conductive layer. In addition to single active layer electrophotographic recording elements, various multi-active electrophotographic recording elements are known. Such elements are sometimes called multi-layer or multi-active-layer elements because they contain at least two active layers that interact to form an electrostatic latent image.
Compositions comprising a polycarbonate resin having a photoconductor dispersed therein have been known for use in photoconductive layers of photoconductor elements of the type employable for use in electrophotographic processes. For example, U.S. Pat. No. 3,615,414 teaches multiphase heterogeneous compositions of a photoconductor, a thiapyrylium dye and a polycarbonate.
These compositions suffer from the disadvantage that the nonpolymeric photoconductors therein tend to be leachable by solvents, such as the solvents used in liquid toner developers.